This is a great question. It is a bit scandalous, just to warn you. Also keep in mind that ancient sources must be taken with a grain of salt.

According to Josephus, the Jewish historian, Decius Mundus, a prominent Roman knight, was obsessed with a Roman noble woman named Paulina. He often approached her for one night of intimacy in exchange for an enormous amount of money. Upright Paulina refused every time. Decius, repeatedly rebuffed and now dejected, planned to starve himself to death.

At this point, a freedwoman named Ida approached Decius with a plan. She plotted to use Paulina’s religious commitment to the Isis cult, in order to deceive her into sleeping with Decius. Decius agreed to this plot. Ida sent a priest of Isis to Paulina’s house and had him tell her that the god, Anubis, wanted to see her. In the meantime, Decius was waiting for her in the temple in the guise of Anubis. As the story goes, Decius slept with Paulina, but he was not reticent about his action.

Upon seeing Paulina, Decius divulged what had happened. Paulina, outraged, told her husband, who brought the matter to the emperor, Tiberius. Tiberius summarily crucified Ida along with the priest, and exiled Decius along with the Isiacs.

According to Josephus, the reason for the action against the Isis cult was immorality. The corrupt practices of the Isiacs had to be addressed. The social fabric of the Rome was at stake. To be sure